#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main(void)
{
	int a = 0 ;
	double sum = 0;
	scanf("%d", &a);
	for (int j = a; j>0; j--){
		sum += 1.0/ (1 + 2 * (j - 1));
	}

	printf("sum = %.6lf", sum);
	return 0;
}